1. Field of the Invention
The present invention relates to a flexible multilayer wiring board applied to a sheet switch used for a thin-type panel switch of vehicle-mounted or home electric equipment.
2. Description of the Related Art
To explain the configuration of a conventional type flexible multilayer wiring board referring to FIG. 19, the conventional type flexible multilayer wiring board is formed by mainly bonding a first flat flexible base material 110 and a second flat flexible base material 120 via an adhesive 130, a first conductive pattern 111 is provided on the unbonded surface of the first flexible base material 110 and a second conductive pattern 121 is provided on the unbonded surface of the second flexible base material 120.
A through hole 113 is formed in the first flexible base material 110, a through hole 123 is formed in the second flexible base material 120, both the through holes 113 and 123 mutually conduct, gold plate 140 is provided to their inner walls and the first conductive pattern 111 and the second conductive pattern 121 conduct.
The first flexible base material 110 is formed by a flat film substrate made of polyimide, the first conductive pattern 111 made of copper foil is formed on the back surface by etching and gold plate 112 is laminated on the first conductive pattern 111 by electrolytic plating.
The second flexible base material 120 is also similarly formed by a flat film substrate made of polyimide, the second conductive pattern 121 made of copper foil is formed on the surface by etching and gold plate 122 is laminated on the second conductive pattern 121 by electrolytic plating.
The first flexible base material 110 and the second flexible base material 120 are bonded via the adhesive 130 provided between them.
At this time, the through holes 113 and 123 are opposed and conduct, the gold plate 140 is provided to the inner walls of these through holes 113 and 123 and is also extended on the reverse side to the through holes 113 and 123.
The first conductive pattern 111 and the second conductive pattern 121 conduct via this gold plate 140.
The conventional type flexible multilayer wiring board is manufactured by forming the first conductive pattern 111 on the first flexible base material 110 in a desired shape by etching, laminating the gold plate 112 on it by electrolytic plating and afterward, punching the through hole 113 by a press.
The second flexible base material 120 is also similarly manufactured by forming the second conductive pattern 121, the gold plate 122 and the through hole 123.
Afterward, the adhesive 130 is provided to at least one wiring board by desired means such as printing and both base materials are bonded.
Afterward, when the gold plate 140 is applied to the inner wall of the through holes 113 and 123 which mutually communicate by electrolytic plating and the like, and the first conductive pattern 111 and the second conductive pattern 121 conduct, the conventional type flexible multilayer wiring board is completed. As the first and second conductive patterns 111 and 121 are formed by etching, the gold plates 112 and 122 are respectively laminated on the first and second conductive patterns 111 and 121 by electrolytic plating and gold plating is also applied to the through holes 113 and 123, the conventional type flexible multilayer wiring board has a problem that the cost is increased because the processes are complex and in addition, gold plating is used.
As gold plate 140 is applied to the inner wall of the through holes 113 and 123, the reliability of the conduction of the first and second conductive patterns 111 and 121 may have a problem depending upon a state in which the gold plate adheres.
Then, the object of the invention is to provide a flexible multilayer wiring board of which the productivity is satisfactory, which is low-priced and highly reliable in connection.
For first solvable means for solving the above-mentioned problems, first and second flexible base materials of which each one surface is bonded via an adhesive and a first conductive body that electrically connects a first conductive pattern formed on the unbonded surface of the first flexible base material with a second conductive pattern formed on the second flexible base material are provided, the first flexible base material is provided with a first through hole and a connection which is formed around the first through hole on the side of the unbonded surface and which conducts with the first conductive pattern, space is provided between the periphery on the side of the bonded surface of the first through hole of the first flexible base material and the second flexible base material, an air path via which air in the space can escape is provided between the first and second flexible base materials, conductive paste forming the first conductive body is filled in the space via the first through hole, the connection and the second conductive pattern are electrically connected and when the conductive paste is filled in the space, air in the space escapes via the air path.
For second solvable means, the air path is formed by a part where the adhesive is not formed.
For third solvable means, an air port of the air path is provided at the peripheral end of at least one of the first flexible base material and the second flexible base material.
For fourth solvable means, the air port of the air path is provided to a mounting hole provided to mount the first and second flexible base materials.
For fifth solvable means, the second conductive pattern is formed on the side of the bonded surface of the second flexible base material and the first conductive body is touched to at least a part of the second conductive pattern.
For sixth solvable means, the second conductive pattern is formed on the side of the unbonded surface of the second flexible base material, a second through hole is provided in a position opposite to the first through hole in the second flexible base material, a second conductive body is filled in the second through hole, and the first and second conductive patterns conduct via the second conductive body.
For seventh solvable means, the first conductive body is formed by the screen printing of conductive paste.
For eighth solvable means, an insulating resist layer is respectively provided on the side of each bonded surface of the first and second flexible base materials and these resist layers are bonded via the adhesive.